1. Field of the Invention
The present invention relates to an optical pickup actuator having a slim and lightweight structure which performs a tilting operation in a limited space while a driving force thereof is maximized, and an optical recording and/or reproducing apparatus using the same.
2. Description of the Related Art
In general, optical pickups are embedded in an optical recording and/or reproducing apparatus, move in a radial direction of a disc used as a recording medium, and record and/or reproduce information on/from the disc in a non-contact manner. Such optical pickups include an actuator which drives an objective lens in tracking and focusing directions of the disc such that an optical spot is irradiated in a desired track position of the disc. Portable personal computers (PCs) such as notebooks, should be thin and lightweight, resulting in spatial limitations in the entire system. Thus, an actuator embedded in such PCs should also be slim. A reflection mirror is embedded in the optical pickups so that light faces an objective lens. In order to meet the needs of a slim actuator, an asymmetrical actuator in which the driving axis of the actuator and the optical axis of the objective lens are differently placed, has been proposed such that a distance between the objective lens and the reflection mirror of the optical pickups is reduced. An example thereof is disclosed in U.S. Pat. No. 5,684,645.
Referring to FIGS. 1 and 2, a conventional optical pickup actuator 10 includes a holder 14 placed at one side of the optical pickup actuator 10, a focusing coil 18 wound along the circumference of a bobbin 12 having a first guide groove 16a in the center of the bobbin 12, and a pair of tracking coils 15 placed at one side of the bobbin 12. The optical pickup actuator 10 further includes a second guide groove 16b formed in a moving portion 17 having an objective lens 11 mounted at one side of the moving portion 17, and the bobbin 12 is embedded in the second guide groove 16b. Here, a U-shaped yoke 31 is embedded through the first guide groove 16a and the second guide groove 16b, and a magnet 32 is mounted at an internal side of the U-shaped yoke 31 such that the pair of tracking coils 15 are opposite to the focusing coil 18.
The focusing coil 18 may be divided into a portion 18a wound at the inside of the U-shaped yoke 31, and a portion 18b wound at the outside of the U-shaped yoke 31. An effective coil portion to which a force generated by the magnet 32 can be applied is only a focusing coil 18a wound at the inside of the U-shaped yoke 31, and a focusing coil 18b wound at the outside of the U-shaped yoke 31 does not contribute to driving in a focusing direction. Thus, compared to the length of the focusing coil 18, power consumption is large, a driving force is small, and the volume of the conventional actuator is big.
The moving portion 17 is movably supported by a pair of wires 13a and 13b having one end fixed on the holder 14 and the other end fixed at both sides of the moving portion 17. The moving portion 17 and the bobbin 12 are movably coupled to each other. If current is applied to the focusing coil 18 and the tracking coils 15, a force is applied to the tracking coils 15 and the focusing coil 18 by electromagnetic interaction of the magnet 32, the focusing coil 18, and the tracking coils 15, and thereby the moving portion 17 works together with the bobbin 12. The direction in which a force is applied to the focusing coil 18 and the tracking coils 15 follows Flemings' left hand rule.
If an electromagnetic force is applied to the focusing coil 18 and the tracking coils 15 by interaction of the focusing coil 18, the tracking coil 15, and the magnet 32, the moving portion 17 moves in a focusing direction F or tracking direction T. As a result, the objective lens 11 mounted on the moving portion 17 moves, and thus a position in which an optical spot is formed on a disc (not shown) is adjusted.
In the above structure, the objective lens 11 is arranged at the circumference of the actuator 10 while the reflection mirror may be placed under the objective lens 11, thereby obtaining a slim optical pickup. Further, in order to meet the needs of a slim and lightweight optical pickup, a fine pattern coil (FPC) instead of a winding coil may be used as a focusing coil and a tracking coil. In order to increase a driving force in asymmetrical actuators and obtain slim asymmetrical actuators, the structure of a magnetic circuit having an FPC and a magnet needs to be studied.  As optical pickups become slim, it is not easy to couple the pair of wires 13a and 13b to the moving portion 17. To drive in the focusing direction, tracking direction, and tilting direction, a conventional actuator has six wires. Further, four-axis drive actuators which drive in the focusing direction, tracking direction, radial tilting direction, and track tilting direction require more wires. In this case, there are spatial limitations when a plurality of wires are installed in a very narrow space. As the number of wires is increased, it is very difficult to perform a process of attaching the wires, and thus a defective rate during the manufacturing of drive actuators is increased.